The present disclosure relates to a backside illuminated image sensor and a method of manufacturing the same.
An image sensor is a semiconductor device that converts an optical image into electrical signals. Image sensors known in the art include charge coupled devices (CCDs) and CMOS image sensors.
CMOS image sensors include unit pixels, each including a photodiode and metal-oxide-semiconductor (MOS) transistors. CMOS image sensors can sequentially detect the electrical signals of the unit pixels using a switching method in order to form an image. CMOS image sensors can be front side illuminated image sensors or backside illuminated image sensors.
A front side illuminated (or front-illuminated) image sensor may include photodiodes formed in a substrate, transistors formed on a front surface of the substrate, wiring layers formed on the front surface of the substrate, and a color filter layer and micro lens array formed on the wiring layers.
In contrast, a backside illuminated (or back-illuminated) sensor can arrange the wiring behind the photodiode layer. Backside illuminated image sensor therefore have an improved light-receiving efficiency in comparison with front side illuminated image sensors. Backside illuminated image sensors can, however, be more difficult to manufacture, resulting in lower yields and higher prices.
One manufacturing difficulty can result from a bonding pad formed on an insulating layer. The bonding pad may be connected with the wiring layers on the front surface of the substrate by a contact passing through the substrate and the insulating layer. However, when the bonding pad has a relatively thin thickness, the bonding pad may be damaged or peeled away from the substrate during the wire bonding process.